An example of such an article storage racks is disclosed in JP Publication of Application No. 2002-252277 (Patent Document 1). The article storage rack of Patent Document 1 is installed in a clean room, and is provided to store containers for holding a plurality of semiconductor substrates (see Paragraph [0033] of Patent Document 1). The rack has plate-shaped top boards 5 extending along the horizontal plane as shown in FIG. 1 of Patent Document 1.
Formed in each top board 5 of the article storage rack of Patent Document 1 is a cut-out portion which provides an opening along the vertical direction that opens in the direction (projecting direction) in which the top board 5 projects. The cut-out portion is so dimensioned that a movable support member of a transfer device which supports a container to be stored can pass through the opening along the vertical direction. The article storage rack of Patent Document 1 can transfer a container from the movable support member to the rack by moving the movable support member which is supporting the container from a position above the top board 5 to a position below the top board 5 through the cut-out portion. In addition, the article storage rack of Patent Document 1 can transfer a container from the rack to the movable support member by moving the movable support member which is not supporting any container from a position below the top board 5 to a position above the top board 5 through the cut-out portion. The structural strength of the top board 5 is weakened because such a cut-out portion is formed. In order to reinforce each top board 5, supporting ribs 6 which support the top board 5 from below are provided in the article storage rack of Patent Document 1.
In the article storage rack of Patent Document 1, a plurality of columns 3 which project in the projecting direction with respect to a reference surface, and which are spaced apart from one another along a lateral or right and left direction which is horizontal and is perpendicular to the projecting direction. And article storing areas for storing articles are formed between two columns 3 that are adjacent each other along the lateral direction. The proximal end portion of each supporting rib 6 is attached to a corresponding column 3 at a position that is offset or displaced from the reference surface in the projecting direction. In addition, in order to support the weight of the container properly, the distal end side portion of each supporting rib 6 is located at a position that overlaps with the area in which the article exists as seen along the vertical direction.